It is the first UK printing. The first 4 UK Dark Tower books were only printed in paperback. The first 3 by Sphere, and the 4th by Hodder. (The 4th one in hardback is Australian)

Its very common, and can be found in mint condition. Your one is not so great condition and probably worth less. They come up on ebay quite often. On a good day, with the wind in the right direction, you may gat £15 for it.